Science Buddies: "Ask an Expert"

i have tried to create a minirail gun of my own, and i am working with a 0.5 tesla magnet... with around 13 volts. mine is a different model differing from th econventional rail gun we see that uses capacitors and stuff. i am using a metal bll bearing, pretty light, and i am not sure what material its made of, but i know that its non-magnetic. ok, hte problem is that everytime i flip the switch, there is a big burst of sparks, poisonous white smoke, and i find that the bearing has melted with the copper foils i am using as rails.. and the fuse gets tripped... what can i do? time is running out, and i am getting quite helpless...

Hi,

Your project sounds very interesting, but are you trying just to build something or are you testing different rail gun desings? I don't know much about rail guns, I only know some about accelerators and x-ray machines, but it sounds like you're having electrical arcing. You might try checking your electrical work to make sure you aren't shorting anything out.

I would be very careful since you are working with high voltage and high amperage. Also, you mentioned a poisonous white smoke. If that's the case, then I'd recommend either having a professional look at it in person and make sure it is safe, or change your project to a simpler, safer one.

Please let us know how it goes,
Philip

hi..

thanks for your reply Philip, but i was wondering whether the current is enough; the magnet, i feel is strong enough. As far as i am aware, i have not short- circuited the apparatus. As for the electrical arcing, its just a spark, not a prolonged one, so it cannot be arcing, can it? I'm not really looking at different designs, i'm just working on this particular one. the design's different because it doe not require an armature or anything, and i am attempting to use Fleming's lefft hand rule, instead of Lorentz's force or whatever. I'm really afraid that I won't get an observable result with the magnitudes of magnetic stregth and current i'm working with. Do you have an opinion on this please? By the way, I also have a proposal, that i am trying to upload as an attachment. It sounds ambitious though!!

Hi Prav,

I'm sorry for the delay. I'm afraid I'm no knowledgeable enough to help you, so I'll forward your question to some other experts that know more about rail guns so they can help you more.

I Googled for "voltage rail gun" and found this site- http://home.insightbb.com/~jmengel4/rai ... intro.html Towards the bottom of the page it has an equation for the speed of the projectile based on amperes, magnetic strength, and a few others. You should be able to use this equation to determine if you have the correct amount of amperes running through it.

This is just an opinion, but I think you should be able to have observable data, even with a smaller ray gun. I'l recommend using a smaller projectile so that you will see changes more clearly, and if you don't see any data, then I would suggest using smaller-range instruments for measuring. But I don't think you will have a problem.

Your proposal sounds very good and well thought out. Could you tell me what power supply your using and how many amps it supplies?

Thanks and please keep us updated,
Philip

Any spark is a sign that your circuit is not well enough insulated, and yes even a small spark can discharge enough of your power to make the entire tool useless or severely skew your results.

You need to insulate it well enough that it does not spark. I do not know if it will perform well even with insulation, but if you're throwing sparks there is no way you've got control of this experiment well enough to distinguish between designs. It's an extra variable (how much is discharged when it sparks? You can't know)

Hi,

You might try a non-metallic projectile. This is common is testing real high-speed guns (cold gas or rail) because the acceleration can be high enough to overcome the crystal binding forces of the metal. You don't have that problem but it is a justification for trying a non-metallic projectile. Fiberglass is often used.